5

enter image description here

A solution I saw somewhere suggested to use

\usepackage{bbold}
$\mathbb{1}$

which works well and I get what I want. However, now other symbols used to represent real numbers, natural numbers, etc look ugly.

ugly symbols

I'd like them to look (without using bbold)

not ugly symbols

I'd like to only use that package to achieve that strange double one. Is there any way I can do that?

5

How about dsfont?

\documentclass{article}
\usepackage{dsfont}
\usepackage{amssymb}
\begin{document}
$\mathds{1}$ and $\mathbb{B}$ or $\mathds{B}$
\end{document}

enter image description here

5

The modern toolchain, with unicode-math, lets you select any TrueType or OpenType font for blackboard bold, or any subset of blackboard bold. For example,

\setmathfont[Scale = MatchUppercase, range=\Bbbone]{XITS Math}

changes only that one symbol, while

\setmathfont[Scale = MatchUppercase, range=bb]{STIX Two Math}

changes the entire blackboard bold alphabet.

3

You can just borrow the glyph from the bbold font.

\documentclass{article}
\usepackage{amsmath,amssymb}

\newcommand{\bbone}{\text{\usefont{U}{bbold}{m}{n}1}}
\MakeRobust{\bbone}

\begin{document}

$\bbone\in\mathbb{R}$

\end{document}

enter image description here

The “robustness” is needed for uses in moving arguments (sectional titles or captions).

1
  • I am smiling for your answer because I remember that you did not like the number one of dsfont in my book. :-).+1 for all answers and the question. – Sebastiano Jun 7 '20 at 10:53

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